Resize your picture in correct dimensions like 64x64 or 256x256 or so on. Save it in .bmp file. Then go ahead in TXD Workshop make new file, import your resized picture in it and double click on it, name it and tick directx box in. Export your texture as .txd file and in short you are done.
edit: oh my bad you are asking textdraws not textures lmao. Well... not quite sure, but i believe its pretty much same only gotta make an alpha picture, so the main picture goes in opacity mode.